Preservative efficacy of selected antimicrobials of natural origin in a cosmetic emulsion

Abstract Objective To investigate the efficacy of 13 antimicrobial substances (11 substances of natural origin and two conventional preservatives as controls) at two concentrations in an o/w cosmetic emulsion. Methods Cosmetic formulations were analysed for total aerobic bacterial count and total combined yeast count according to the European Pharmacopoeia 8.0. Challenge tests were performed according to the ISO 11930 standard. Results The total aerobic bacterial count, the total combined yeast count and the total aerobic mesophilic microorganisms were below the acceptable limit for all cosmetic formulations. Challenge test criterion A was fulfilled by all antimicrobials of natural origin, except levulinic acid in the challenge test with Candida albicans , Lactobacillus ferment in the challenge test with C. albicans and Pseudomonas aeruginosa , and grapefruit seed extract in the challenge test with C. albicans . Phenoxyethanol and the combination of methylparaben and propylparaben were inefficient at the minimum studied concentrations. Conclusion The results offer important comparative data on the level of preservative efficacy within the group of antimicrobials of natural origin and in reference to some typical, widely used conventional preservatives. Further research must be encouraged regarding cosmetic over‐preservation.